Blowtorch Parasound upgrade?

[Skorpio]

Inspired by the Blowtorch thread and the importance of the powersupply I have been wondering about upgrading my Parasound P/LS-1100 preamp.

It is a farly old design, and some things may have changed since then. Especially all the parallel capacitors.

All capacitors are bypassed by 4-5 different value film caps, both in main PSU and locally. This is a lot of extra caps!

It will be easy to remove some of them, but what will happen to the sound?

And what types will be best to remove?

My starting point is to remove all, but the electrolytic cap in all places...we are talking about aprox. 76 caps...

Any other relevant upgrades?

[jacco vermeulen]

Eeh,
if you mean P/LD-1100 i'd start by janking out about 30 white blocks, plus the yellow axial stuff underneith them.

[Skorpio]

Yes, that's the one!

Have you tried the mod and what are the results?

[myhrrhleine]

Trust your precision Mk-I ears.
make a change... listen

[jacco vermeulen]

Originally posted by Skorpio
other relevant upgrades

-Transformer, late models have a shielded one. The amp channels are on separate boards, consider adding a 2nd transformer.
There's room in the 1100/1500 models to make a subcompartment for the transformer by putting an alloy bulkhead between the transformer and the boards.
Mr Curl's preferred Hitachi MOSFET output stages are biased at a high quiescent current level, as they should be, and love the cleanest rails.
Steenoe just acquired a bunch of NOS high value Rifa PFE216 polystyrene caps, you could ask him for a couple and solder 1 at each rail of the amp boards instead of the white MKP biggies.
In my stupid opinion, PFE216 caps are not inferior to Mr Curl's favorate RelCap RT.

-Input selector, with a little surgery you could change the c-mos switching to relay operation as in the P/LD-2000.

[Skorpio]

Originally posted by jacco vermeulen


-Transformer, late models have a shielded one. The amp channels are on separate boards, consider adding a 2nd transformer.
There's room in the 1100/1500 models to make a subcompartment for the transformer by putting an alloy bulkhead between the transformer and the boards.
Mr Curl's preferred Hitachi MOSFET output stages are biased at a high quiescent current level, as they should be, and love the cleanest rails.
Steenoe just acquired a bunch of NOS high value Rifa PFE216 polystyrene caps, you could ask him for a couple and solder 1 at each rail of the amp boards instead of the white MKP biggies.
In my stupid opinion, PFE216 caps are not inferior to Mr Curl's favorate RelCap RT.

-Input selector, with a little surgery you could change the c-mos switching to relay operation as in the P/LD-2000.

Thank you for your input!

Af I understand you correct I shall remove all non-electrolytic decoupling and replace the last electrolytics with RIFA PFE216?

The P/LS-2000 uses IRF510/9510 output bufferes, is that because they are better?
Do you know what the standard Iq must be?

The input switching is ok, when using the direct input (relay)

The is also relay on output. I think I will bypass it on output 1 and leave it in on output 2.

From MOS-FET output, signal is passing 100R/2w resistor, relay and then 100R resistor again.
Could they be bypassed?

200R in series with output is also not in line with spec. saying Rout=60R?

Perhaps I should leave on in for oscillation prevention?


Also considering resistor change the following places:

-Input series resistor, 1k
-Feedback resistor, 1k
-Output series resistors 2x 100R

But I will do that later, after PSU change....

[jacco vermeulen]

Originally posted by Skorpio
The P/LS-2000 uses IRF510/9510 output buffers.

Likely cheaper to match, the P/LD-2000 has Mr Curl's balanced complementary design, = 4 matched output devices/ch.
At the expense of a bigger heatsink, the ones in 2000 (and the P/LD-1500) are a lot larger than those of the P/LD-1100.
2SJ7*/2SK21* have always been expensive, but vertical MOSFET prices dropped dramatically over the years. (i recall having had to pay +€5 each for a decent TO-220 vertical in the '80s)
The current JC-2 has the 510/9510 in the output stage as well.

Laterals can be biased from 25mA up, to sound any good starts at 50mA, imo.
The heatsink in the 1100 can easily handle a couple of watts at 40C inside the chassis.